Display device

ABSTRACT

Disclosed is a display device that with low power consumption. The display device includes a first thin film transistor having a polycrystalline semiconductor layer in an active area and a second thin film transistor having an oxide semiconductor layer in the active area, wherein at least one opening disposed in a bending area has the same depth as one of a plurality of contact holes disposed in the active area, whereby the opening and the contact holes are formed through the same process, and the process is therefore simplified, and wherein a high-potential supply line and a low-potential supply line are disposed so as to be spaced apart from each other in the horizontal direction, whereas a reference line and the low-potential supply line are disposed so as to overlap each other, thereby preventing signal lines from being shorted.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Republic of Korea PatentApplication No. 10-2017-0175083, filed on Dec. 19, 2017, which is herebyincorporated by reference in its entirety.

BACKGROUND Field of Technology

The present disclosure relates to a display device, and moreparticularly to a display device that is capable of realizing low powerconsumption.

Discussion of the Related Art

Image display devices, which are a core technology in the informationand communication age and serve to display various kinds of informationon a screen, have been developed such that the image display devices arethinner, lighter, and portable and exhibit high performance. As aresult, flat panel display devices that have lower weight and volumethan cathode ray tubes (CRT) have received a great deal of attention.

Representative examples of such flat panel display devices may include aliquid crystal display (LCD) device, a plasma display panel (PDP)device, an organic light-emitting display (OLED) device, and anelectrophoretic display (ED) device.

With the active development of personal electronic devices, portableand/or wearable flat panel display devices have been developed. Adisplay device capable of realizing low power consumption is required inorder to be applied to portable and/or wearable devices. However,display devices developed to date have difficulty in realizing low powerconsumption.

SUMMARY

Accordingly, the present disclosure is directed to a display device thatsubstantially obviates one or more problems due to limitations anddisadvantages of the related art.

An object of the present disclosure is to provide a display device thatis capable of realizing low power consumption.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following, or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the disclosure, as embodied and broadly described herein, adisplay device includes a first thin film transistor having apolycrystalline semiconductor layer in an active area and a second thinfilm transistor having an oxide semiconductor layer in the active area,thereby realizing low power consumption, wherein at least one openingdisposed in a bending area has the same depth as one of a plurality ofcontact holes disposed in the active area, whereby the opening and thecontact holes are formed through the same process, and the process istherefore simplified, and wherein a high-potential supply line and alow-potential supply line, the voltage difference between which islarge, are disposed so as to be spaced apart from each other in thehorizontal direction, whereas a reference line and the low-potentialsupply line, the voltage difference between which is small, are disposedso as to overlap each other, thereby preventing signal lines from beingshorted.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the disclosure and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the disclosure andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 is a plan view showing a display device according to the presentdisclosure;

FIG. 2 is a sectional view showing the display device taken along lineI-I′ of FIG. 1 according to present disclosure;

FIGS. 3A and 3B are plan views showing subpixels disposed in an activearea shown in FIG. 1 according to present disclosure;

FIGS. 4A and 4B are plan views showing embodiments of a signal linkdisposed in a bending area shown in FIG. 1 according to presentdisclosure;

FIG. 5 is a circuit diagram illustrating each subpixel of the displaydevice shown in FIG. 1 according to present disclosure;

FIG. 6 is a plan view showing the subpixel shown in FIG. 5 according topresent disclosure;

FIG. 7A is a sectional view showing an organic light-emitting displaydevice taken along lines II-II′ and III-III′ of FIG. 6, and FIG. 7B is asectional view showing an organic light-emitting display device takenalong lines IV-IV′, and V-V′ of FIG. 6 according to the presentdisclosure;

FIG. 8 is a sectional view showing another embodiment of a bending areashown in FIG. 7 according to the present disclosure; and

FIGS. 9A to 9M are sectional views illustrating a method ofmanufacturing the organic light-emitting display device shown in FIG. 7.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the embodiments of the presentdisclosure, examples of which are illustrated in the accompanyingdrawings.

FIG. 1 is a plan view showing a display device according to the presentinvention, and FIG. 2 is a sectional view showing the display deviceaccording to the present disclosure.

The display device shown in FIGS. 1 and 2 includes a display panel 200,a scan driver 202, and a data driver 204.

The display panel 200 is divided into an active area AA provided on asubstrate 101 and a non-active area NA disposed around the active areaAA. The substrate 101 is made of a plastic material that exhibits highflexibility, by which the substrate 101 is bendable. For example, thesubstrate 101 may be made of polyimide (PI), polyethylene terephthalate(PET), polyethylene naphthalate (PEN), polycarbonate (PC), polyethersulfone (PES), polyacrylate (PAR), polysulfone (PSF), or cyclic olefincopolymer (COC).

The active area AA displays an image through unit pixels arranged in amatrix form. Each unit pixel may include red (R), green (G), and blue(B) subpixels. Alternatively, each unit pixel may include red (R), green(G), blue (B), and white (W) subpixels. For example, as shown in FIG.3A, the red (R), green (G), and blue (B) subpixels may be arranged alongthe same imaginary horizontal line. Alternatively, as shown in FIG. 3B,the red (R), green (G), and blue (B) subpixels may be spaced apart fromeach other so as to form an imaginary triangular structure.

Each subpixel includes at least one of a thin film transistor having anoxide semiconductor layer or a thin film transistor having apolycrystalline semiconductor layer. A thin film transistor having anoxide semiconductor layer and a thin film transistor having apolycrystalline semiconductor layer exhibit higher electron mobilitythan a thin film transistor having an amorphous semiconductor layer.Consequently, it is possible to realize high resolution and low powerconsumption.

At least one of the data driver 204 or the scan driver 202 may bedisposed in the non-active area NA.

The scan driver 202 drives scan lines of the display panel 200. The scandriver 202 is configured using at least one of a thin film transistorhaving an oxide semiconductor layer or a thin film transistor having apolycrystalline semiconductor layer. The thin film transistor of thescan driver 202 is simultaneously formed in the same process as that forforming at least one thin film transistor disposed at each subpixel inthe active area AA.

The data driver 204 drives data lines of the display panel 200. The datadriver 204 is mounted on the substrate 101 in the form of a chip, or ismounted on a signal transport film 206 in the form of a chip. The datadriver 204 is attached to the non-active area NA of the display panel200. As shown in FIGS. 4A and 4B, a plurality of signal pads PAD aredisposed in the non-active area NA so as to be electrically connected tothe signal transport film 206. Drive signals generated from the datadriver 204, the scan driver 202, a power supply unit (not shown), and atiming controller (not shown) are supplied to signal lines disposed inthe active area AA via the signal pads PAD.

The non-active area NA includes a bending area BA that enables thedisplay panel 200 to be bent or folded. The bending area BA is an areathat is bent in order to locate non-display areas, such as the signalpads PAD, the scan driver 202, and the data driver 204, on the rearsurface of the active area AA. As shown in FIG. 1, the bending area BAis disposed in the upper part of the non-active area NA, which islocated between the active area AA and the data driver 204.Alternatively, the bending area BA may be disposed in at least one ofthe upper, lower, left, or right part of the non-active area NA.Consequently, the area ratio of the active area AA to the entire screenof the display device is maximized, and the area ratio of the non-activearea NA to the entire screen of the display device is minimized.

A signal link LK disposed in the bending area BA connects the signalpads PAD with the signal lines disposed in the active area AA. In thecase in which the signal link LK is formed in a straight line in thebending direction BD, the greatest bending stress may be applied to thesignal link LK, whereby the signal link LK may be cracked or cut.According to the present disclosure, therefore, the signal link LK isconfigured to have a wide area in the direction that intersects thebending direction BD in order to minimize the bending stress applied tothe signal link LK. To this end, as shown in FIG. 4A, the signal link LKmay be formed in a zigzag shape or in the shape of a sine wave.Alternatively, as shown in FIG. 4B, the signal link LK may be formed ina shape in which a plurality of hollow diamonds is connected in a line.

In addition, as shown in FIG. 2, at least one opening 212 is disposed inthe bending area BA such that the bending area BA can be easily bent.The opening 212 is formed by removing a plurality of inorganicdielectric layers 210, which are disposed in the bending area BA andform cracks in the bending area BA. Specifically, when the substrate 101is bent, bending stress is continuously applied to the inorganicdielectric layers 210 disposed in the bending area BA. Since theinorganic dielectric layers 210 exhibit lower elasticity than an organicdielectric material, cracks may be easily formed in the inorganicdielectric layers 210. The cracks formed in the inorganic dielectriclayers 210 spread to the active area AA along the inorganic dielectriclayers 210, which leads to line defects and device-drivingdeterioration. Consequently, at least one planarization layer 208, madeof an organic dielectric material that exhibits higher elasticity thanthe inorganic dielectric layers 210, is disposed in the bending area BA.The planarization layer 208 may reduce bending stress generated when thesubstrate 101 is bent, whereby the formation of cracks may be prevented.The opening 212 in the bending area BA is formed through the same maskprocess as that for forming at least one of a plurality of contact holesdisposed in the active area AA, whereby the structure and process may besimplified.

A display device having a simplified structure and process may beapplied to a display device that requires a thin film transistor, suchas a liquid crystal display device or an organic light-emitting displaydevice. Hereinafter, an embodiment of the present disclosure in which adisplay device having a simplified structure and process is applied toan organic light-emitting display device will be described.

As shown in FIG. 5, each subpixel SP of the organic light-emittingdisplay device includes a pixel-driving circuit and a light-emittingdevice 130 connected to the pixel-driving circuit.

As shown in FIG. 5, the pixel-driving circuit may be configured to havea 4T1C structure having four thin film transistors ST1, ST2, ST3, and DTand a storage capacitor Cst. Here, the structure of the pixel-drivingcircuit is not limited to the structures shown in FIG. 5. Various kindsof pixel-driving circuits may be used.

The storage capacitor Cst of the pixel-driving circuit shown in FIG. 5is connected between a gate node Ng and a source node Ns in order tomaintain voltage between the gate node Ng and the source node Ns uniformduring a light emission period. The drive transistor DT includes a gateelectrode connected to the gate node Ng, a drain electrode connected toa drain node Nd, and a source electrode connected to the light-emittingdevice 130. A drive transistor DT controls the magnitude of drivecurrent based on voltage between the gate node Ng and the source nodeNs. The light-emitting device 130 is connected between the source nodeNs, which is connected to the source electrode of the drive transistorDT, and a low-potential supply line 162 in order to emit light based ondrive current.

The first switching transistor ST1 shown in FIGS. 5 and 6 includes agate electrode 152 connected to a first scan line SL1, a drain electrode158 connected to a source node Ns, a source electrode 156 connected to adata line DL, and a semiconductor layer 154 that forms a channel betweenthe source and drain electrodes 156 and 158. The first switchingtransistor ST1 is turned on in response to a scan control signal SC1from the first scan line SL1 in order to supply data voltage Vdata fromthe data line DL to the source node Ns.

The second switching transistor ST2 includes a gate electrode GEconnected to a second scan line SL2, a drain electrode DE connected to areference line RL, a source electrode SE connected to a gate node Ng,and a semiconductor layer ACT that forms a channel between the sourceand drain electrodes SE and DE. The second switching transistor ST2 isturned on in response to a scan control signal SC2 from the second scanline SL2 in order to supply a reference voltage Vref from the referenceline RL to the gate node Ng.

The third switching transistor ST3 includes a gate electrode GEconnected to an emission control line EL, a drain electrode DE connectedto the drain node Nd, a source electrode SE connected to thehigh-potential supply line 172, and a semiconductor layer ACT that formsa channel between the source and drain electrodes SE and DE. The thirdswitching transistor ST3 is turned on in response to an emission controlsignal EM from the emission control line EL in order to supplyhigh-potential voltage VDD from the high-potential supply line 172 tothe drain node Nd.

Each of the high-potential supply line 172 and the low-potential supplyline 162, which are included in the pixel-driving circuit, is formed ina mesh shape so as to be shared by at least two subpixels. To this end,the high-potential supply line 172 includes first and secondhigh-potential supply lines 172 a and 172 b, and the low-potentialsupply line 162 includes first and second low-potential supply lines 162a and 162 b.

Each of the second high-potential supply line 172 b and the secondlow-potential supply line 162 b is disposed parallel to the data lineDL, and is provided for at least two subpixels.

The first high-potential supply line 172 a is electrically connected tothe second high-potential supply line 172 b, and is arranged parallel tothe scan line SL. The first high-potential supply line 172 a divergesfrom the second high-potential supply line 172 b so as to intersect thesecond high-potential supply line 172 b. Consequently, the firsthigh-potential supply line 172 a compensates for the resistance of thesecond high-potential supply line 172 b in order to minimize the voltagedrop (IR drop) of the high-potential supply line 172.

The first low-potential supply line 162 a is electrically connected tothe second low-potential supply line 162 b, and is arranged parallel tothe scan line SL. The first low-potential supply line 162 a divergesfrom the second low-potential supply line 162 b so as to intersect thesecond low-potential supply line 162 b. Consequently, the firstlow-potential supply line 162 a compensates for the resistance of thesecond low-potential supply line 162 b in order to minimize the voltagedrop (IR drop) of the low-potential supply line 162.

Since each of the high-potential supply line 172 and the low-potentialsupply line 162 is formed in a mesh shape, the number of secondhigh-potential supply lines 172 b and second low-potential supply lines162 b that are disposed in the vertical direction may be reduced. Sincea larger number of subpixels may be disposed in proportion to thereduced number of second high-potential supply lines 172 b and secondlow-potential supply lines 162 b, an aperture ratio and resolution areimproved.

One of the transistors included in the pixel-driving circuit includes apolycrystalline semiconductor layer, and each of the other transistorsincludes an oxide semiconductor layer. For example, each of the firstand third switching transistors ST1 and ST3 of the pixel-driving circuitshown in FIGS. 5 and 6 is constituted by a first thin film transistor150 having a polycrystalline semiconductor layer 154, and each of thesecond switching transistor ST2 and the drive transistor DT isconstituted by a second thin film transistor 100 having an oxidesemiconductor layer 104. According to the present disclosure, asdescribed above, a second thin film transistor 100 having an oxidesemiconductor layer 104 is applied to the drive transistor DT of eachsubpixel, and a first thin film transistor 150 having a polycrystallinesemiconductor layer 154 is applied to the switching transistor ST ofeach subpixel, whereby power consumption may be reduced.

The first thin film transistor 150 shown in FIGS. 6 and 7 includes apolycrystalline semiconductor layer 154, a first gate electrode 152, afirst source electrode 156, and a first drain electrode 158.

The polycrystalline semiconductor layer 154 is formed on a lower bufferlayer 112. The polycrystalline semiconductor layer 154 includes achannel area, a source area, and a drain area. The channel area overlapsthe first gate electrode 152 in the state in which a lower gatedielectric film 114 is interposed there between so as to be formedbetween the first source and first drain electrodes 156 and 158. Thesource area is electrically connected to the first source electrode 156via a first source contact hole 160S. The drain area is electricallyconnected to the first drain electrode 158 via a first drain contacthole 160D. Since the polycrystalline semiconductor layer 154 exhibitshigher mobility than the amorphous semiconductor layer, therebyexhibiting low consumption and high reliability, the polycrystallinesemiconductor layer 154 is suitable for being applied to the switchingtransistor ST of each subpixel and the scan driver 202 that drives thescan line SL. A multi buffer layer 140 and a lower buffer layer 112 aredisposed between the polycrystalline semiconductor layer 154 and thesubstrate 101. The multi buffer layer 140 delays the diffusion ofmoisture and/or oxygen permeating the substrate 101. The multi bufferlayer 140 is formed by alternately stacking silicon nitride (SiNx) andsilicon oxide (SiOx) at least once. The lower buffer layer 112 protectsthe polycrystalline semiconductor layer 154 and blocks the introductionof various kinds of defects from the substrate 101. The lower bufferlayer 112 may be made of a-Si, silicon nitride (SiNx), or silicon oxide(SiOx).

The first gate electrode 152 is formed on the lower gate dielectric film114. The first gate electrode 152 overlaps the channel area of thepolycrystalline semiconductor layer 154 in the state in which the lowergate dielectric film 114 is disposed therebetween. The first gateelectrode 152 may be made of the same material as a storage lowerelectrode 182, such as one of molybdenum (Mo), aluminum (Al), chrome(Cr), gold (Au), titanium (Ti), nickel (Ni), neodymium (Nd), and copper(Cu) or an alloy thereof, and may have a single-layered structure or amulti-layered structure. However, the present disclosure is not limitedthereto.

First and second lower interlayer dielectric films 116 and 118 locatedon the polycrystalline semiconductor layer 154 are made of an inorganicfilm having higher hydrogen particle content than an upper interlayerdielectric film 124. For example, the first and second lower interlayerdielectric films 116 and 118 are made of silicon nitride (SiNx) formedby deposition using NH3 gas, and the upper interlayer dielectric film124 is made of silicon oxide (SiOx). During a hydrogenation process, thehydrogen particles contained in the first and second lower interlayerdielectric films 116 and 118 are diffused to the polycrystallinesemiconductor layer 154, whereby apertures in the polycrystallinesemiconductor layer 154 are filled with hydrogen. Consequently, thepolycrystalline semiconductor layer 154 becomes stabilized, therebypreventing a reduction in the properties of the first thin filmtransistor 150.

The first source electrode 156 is connected to the source area of thepolycrystalline semiconductor layer 154 via the first source contacthole 160S, which is formed through the lower gate dielectric film 114,the first and second lower interlayer dielectric films 116 and 118, anupper buffer layer 122, and the upper interlayer dielectric film 124.The first drain electrode 158 faces the first source electrode 156, andis connected to the drain area of the polycrystalline semiconductorlayer 154 via the first drain contact hole 160D, which is formed throughthe lower gate dielectric film 114, the first and second lowerinterlayer dielectric films 116 and 118, the upper buffer layer 122, andthe upper interlayer dielectric film 124. Since the first source andfirst drain electrodes 156 and 158 are made of the same material as astorage supply line 186 and are formed in the same plane as the storagesupply line 186, the first source and first drain electrodes 156 and 158may be simultaneously formed through the same mask process as that forforming the storage supply line 186.

After activation and hydrogenation of the polycrystalline semiconductorlayer 154 of the first thin film transistor 150, the oxide semiconductorlayer 104 of the second thin film transistor 100 is formed. That is, theoxide semiconductor layer 104 is located on the polycrystallinesemiconductor layer 154. As a result, the oxide semiconductor layer 104is not exposed to a high-temperature atmosphere during the activationand hydrogenation of the polycrystalline semiconductor layer 154.Consequently, damage to the oxide semiconductor layer 104 is prevented,whereby the reliability of the oxide semiconductor layer 104 isimproved.

The second thin film transistor 100 is disposed on the upper bufferlayer 122 so as to be spaced apart from the first thin film transistor150. The second thin film transistor 100 includes a second gateelectrode 102, an oxide semiconductor layer 104, a second sourceelectrode 106, and a second drain electrode 108.

The second gate electrode 102 overlaps the oxide semiconductor layer 104in the state in which an upper gate dielectric pattern 146 is disposedthere between. The second gate electrode 102 is formed in the same planeas the first high-potential supply line 172 a, i.e. on the upper gatedielectric pattern 146, and is made of the same material as the firsthigh-potential supply line 172 a. Consequently, the second gateelectrode 102 and the first high-potential supply line 172 a may beformed through the same mask process, whereby the number of maskprocesses may be reduced.

The oxide semiconductor layer 104 is formed on the upper buffer layer122 so as to overlap the second gate electrode 102 such that a channelis formed between the second source electrode 106 and the second drainelectrode 108. The oxide semiconductor layer 104 is made of an oxideincluding at least one of Zn, Cd, Ga, In, Sn, Hf, or Zr. Since thesecond thin film transistor 100 including the oxide semiconductor layer104 exhibits higher charge mobility and lower leakage of current thanthe first thin film transistor 150 including the polycrystallinesemiconductor layer 154, the second thin film transistor 100 may beapplied to the switching and drive thin film transistors ST and DT, eachof which has a short on time and a long off time.

The upper interlayer dielectric film 124 and the upper buffer layer 122,which are adjacent to the upper part and the lower part of the oxidesemiconductor layer 104, respectively, are made of an inorganic filmthat has lower hydrogen particle content than the lower interlayerdielectric films 116 and 118. For example, the upper interlayerdielectric film 124 and the upper buffer layer 122 may be made ofsilicon oxide (SiOx), and the lower interlayer dielectric films 116 and118 may be made of silicon nitride (SiNx). During heat treatment of theoxide semiconductor layer 104, therefore, hydrogen in the lowerinterlayer dielectric films 116 and 118 and hydrogen in thepolycrystalline semiconductor layer 154 may be prevented from spreadingto the oxide semiconductor layer 104.

The second source and second drain electrodes 106 and 108 may be formedon the upper interlayer dielectric film 124, may be made of one ofmolybdenum (Mo), aluminum (Al), chrome (Cr), gold (Au), titanium (Ti),nickel (Ni), neodymium (Nd), and copper (Cu) or an alloy thereof, andmay have a single-layered structure or a multi-layered structure.However, the present disclosure is not limited thereto.

The second source electrode 106 is connected to a source area of theoxide semiconductor layer 104 via a second source contact hole 110S,which is formed through the upper interlayer dielectric film 124. Thesecond drain electrode 108 is connected to a drain area of the oxidesemiconductor layer 104 via a second drain contact hole 110D, which isformed through the upper interlayer dielectric film 124. The secondsource and second drain electrodes 106 and 108 are formed so as to faceeach other in the state in which a channel area of the oxidesemiconductor layer 104 is disposed there between.

As shown in FIG. 7, a storage lower electrode 182 and a storage upperelectrode 184 overlap each other in the state in which the first lowerinterlayer dielectric film 116 is disposed therebetween in order to forma storage capacitor Cst (180).

The storage lower electrode 182 is connected to one of the second gateelectrode 102 and the second source electrode 106 of the drivetransistor DT. The storage upper electrode 184 is located on the lowergate dielectric film 114, is formed in the same layer as the first gateelectrode 152, and is made of the same material as the first gateelectrode 152.

The storage upper electrode 184 is connected to the other of the secondgate electrode 102 and the second source electrode 106 of the drivetransistor DT via the storage supply line 186. The storage upperelectrode 184 is located on the first lower interlayer dielectric film116. The storage upper electrode 184 is formed in the same layer as alight-blocking layer 178 and the first low-potential supply line 162 a,and is made of the same material as the light-blocking layer 178 and thefirst low-potential supply line 162 a. The storage upper electrode 184is exposed through a storage contact hole 188, which is formed throughthe second lower interlayer dielectric film 118, the upper buffer layer122, and the upper interlayer dielectric film 124, so as to be connectedto the storage supply line 186. Meanwhile, the storage upper electrode184 may be integrally connected to the light-blocking layer 178,although the storage upper electrode 184 is shown in FIG. 7 as beingspaced apart from the light-blocking layer 178.

The first lower interlayer dielectric film 116, which is disposedbetween the storage lower electrode 182 and the storage upper electrode184, is made of an inorganic dielectric material, such as SiOx or SiNx.In one embodiment, the first lower interlayer dielectric film 116 ismade of SiNx, which exhibits higher permittivity than SiOx.Consequently, the storage lower electrode 182 and the storage upperelectrode 184 overlap each other in the state in which the first lowerinterlayer dielectric film 116, which is made of SiNx exhibiting highpermittivity, is disposed there between, whereby the capacitance valueof the storage capacitor Cst, which is proportional to permittivity, isincreased.

The light-emitting device 130 includes an anode 132 connected to thesecond source electrode 106 of the second thin film transistor 100, atleast one light-emitting stack 134 formed on the anode 132, and acathode 136 on the light-emitting stack 134.

The anode 132 is connected to a pixel connection electrode 142, which isexposed through a second pixel contact hole 144, which is formed througha second planarization layer 128. Here, the pixel connection electrode142 is connected to the second source electrode 106, which is exposedthrough a first pixel contact hole 120, which is formed through a firstplanarization layer 126.

The anode 132 is formed to have a multi-layered structure including atransparent conductive film and an opaque conductive film, whichexhibits high reflectance. The transparent conductive film is made of amaterial that has a relatively large work function value, such asindium-tin-oxide (ITO) or indium-zinc-oxide (IZO). The opaque conductivefilm is made of Al, Ag, Cu, Pb, Mo, Ti, or an alloy thereof, and has asingle-layered or multi-layered structure. For example, the anode 132 isformed to have a structure in which a transparent conductive film, anopaque conductive film, and a transparent conductive film aresequentially stacked, or a structure in which a transparent conductivefilm and an opaque conductive film are sequentially stacked. The anode132 is disposed on the second planarization layer 128 so as to overlap acircuit area in which the first and second thin film transistors 150 and100 and the storage capacitor (Cst) 180 are disposed, as well as alight-emitting area defined by a bank 13, whereby the light emissionsize is increased.

The light-emitting stack 134 is formed by a hole-related layer, anorganic light-emitting layer, and an electron-related layer on the anode132 in the forward sequence or in the reverse sequence. In addition, thelight-emitting stack 134 may include first and second light-emittingstacks, which are opposite to each other in the state in which a chargegeneration layer is disposed there between. In this case, the organiclight-emitting layer of one of the first and second light-emittingstacks generates blue light, and the organic light-emitting layer of theother of the first and second light-emitting stacks generatesyellow-green light, whereby white light is generated through the firstand second light-emitting stacks. The white light generated by thelight-emitting stack 134 is incident on a color filter (not shown),which is located on the light-emitting stack 134, whereby a color imagemay be realized. Alternatively, each light-emitting stack 134 maygenerate colored light corresponding to each subpixel without using aseparate color filter in order to realize a color image. That is, alight-emitting stack 134 of a red (R) subpixel may generate red light, alight-emitting stack 134 of a green (G) subpixel may generate greenlight, and a light-emitting stack 134 of a blue (B) subpixel maygenerate blue light.

The bank 138 is formed so as to expose the anode 132. The bank 138 maybe made of an opaque material (e.g. black) in order to prevent opticalinterference between neighboring subpixels. In this case, the bank 138includes a light-blocking material made of at least one of colorpigment, organic black, or carbon.

The cathode 136 is formed on the upper surface and the side surface ofthe light-emitting stack 134 so as to be opposite to the anode 132 inthe state in which the light-emitting stack 134 is disposed therebetween. In the case in which the display device according to thepresent disclosure is applied to a front emission type organiclight-emitting display device, the cathode 136 is made of a transparentconductive film, such as indium-tin-oxide (ITO) or indium-zinc-oxide(IZO).

The cathode 136 is electrically connected to the low-potential supplyline 162. As shown in FIGS. 5B and 6, the low-potential supply line 162includes first and second low-potential supply lines 162 a and 162 b,which intersect each other. As shown in FIG. 7, the first low-potentialsupply line 162 a is formed on the upper gate dielectric pattern 146,which is the same layer as the second gate electrode 102, and is made ofthe same material as the second gate electrode 102. The secondlow-potential supply line 162 b is formed on the first planarizationlayer 126, which is the same layer as the pixel connection electrode142, and is made of the same material as the pixel connection electrode142. The second low-potential supply line 162 b is electricallyconnected to the first low-potential supply line 162 a, which is exposedthrough a first line contact hole 164, which is formed through the upperinterlayer dielectric film 124, and the first planarization layer 126.

As shown in FIGS. 5 and 6, the high-potential supply line 172, whichsupplies high-potential voltage VDD, which is higher than thelow-potential voltage VSS supplied through the low-potential supply line162, includes first and second high-potential supply lines 172 a and 172b, which intersect each other. As shown in FIG. 7, the firsthigh-potential supply line 172 a is formed on the upper gate dielectricpattern 146, which is the same layer as the second gate electrode 102,and is made of the same material as the second gate electrode 102. Thesecond high-potential supply line 172 b is formed on the upperinterlayer dielectric film 124, which is the same layer as the secondsource and second drain electrodes 106 and 108, and is made of the samematerial as the second source and second drain electrodes 106 and 108.The second high-potential supply line 172 b is electrically connected tothe first high-potential supply line 172 a, which is exposed through asecond line contact hole 174, which is formed through the upperinterlayer dielectric film 124.

Since each of the high-potential supply line 172 and the low-potentialsupply line 162 is formed in a mesh shape, the first high-potentialsupply line 172 a and the first low-potential supply line 162 a, whichare arranged in the horizontal direction, are disposed parallel to thescan line SL.

The second high-potential supply line 172 b and the second low-potentialsupply line 162 b, which are arranged in the vertical direction, aredisposed at opposite sides of each subpixel. For example, as shown inFIG. 6, the second low-potential supply line 162 b is disposed at theright side of each subpixel, and the second high-potential supply line172 b is disposed at the left side of each subpixel. The differencebetween the high-potential voltage VDD supplied through the secondhigh-potential supply line 172 b and the low-potential voltage VSSsupplied through the second low-potential supply line 162 b is great. Inthe case in which the second high-potential supply line 172 b and thesecond low-potential supply line 162 b are disposed vertically in thestate in which the first planarization layer 126 is disposed therebetween, dielectric breakdown occurs in the first planarization layer126, whereby the second high-potential supply line 172 b and the secondlow-potential supply line 162 b are shorted. According to the presentinvention, the second high-potential supply line 172 b and the secondlow-potential supply line 162 b are disposed so as to be spaced apartfrom each other in the leftward-rightward direction, whereby it ispossible to prevent the second high-potential supply line 172 b and thesecond low-potential supply line 162 b from being shorted.

The second low-potential supply line 162 b overlaps the reference lineRL in the state in which the first planarization layer 126 is disposedtherebetween. The reference voltage Vref supplied through the referenceline RL and the low-potential voltage VSS supplied through the secondlow-potential supply line 162 b are similar or equal. Consequently,there is no or little voltage difference between the secondlow-potential supply line 162 b and the reference line RL. Inparticular, the difference between the reference voltage Vref suppliedthrough the reference line RL and the low-potential voltage VSS suppliedthrough the second low-potential supply line 162 b is less than thedifference between the high-potential voltage VDD supplied through thesecond high-potential supply line 172 b and the low-potential voltageVSS supplied through the second low-potential supply line 162 b.Consequently, no dielectric breakdown occurs in the first planarizationlayer 126 disposed between the second low-potential supply line 162 band the reference line RL, whereby it is possible to prevent the secondlow-potential supply line 162 b and the reference line RL from beingshorted and thus to prevent a product from catching a fire.

As shown in FIGS. 7A and 7B, a signal link 176, which is connected to atleast one of the low-potential supply line 162, the high-potentialsupply line 172, the data line DL, the scan line SL, or the emissioncontrol line EL, is formed so as to cross the bending area BA, in whichfirst and second openings 192 and 194 are formed. The first opening 192exposes the side surface of the upper interlayer dielectric film 124 andthe upper surface of the upper buffer layer 122. The first opening 192is formed so as to have the same depth d1 as at least one of the secondsource contact hole 110S or the second drain contact hole 110D. Thesecond opening 194 is formed so as to expose the side surfaces of themulti buffer layer 140, the lower buffer layer 112, the lower gatedielectric film 114, the first and second lower interlayer dielectricfilms 116 and 118, and the upper buffer layer 122. The second opening194 is formed so as to have a greater depth d2 than at least one of thefirst source contact hole 160S or the first drain contact hole 160D orto have the same depth d2 as at least one of the first source contacthole 160S or the first drain contact hole 160D. As shown in FIGS. 7A and7B, the sum of the thicknesses of the multi buffer layer 140 and thelower buffer layer 112 has the same thickness as the upper interlayerdielectric film 124 or has a larger thickness than the upper interlayerdielectric film 124. As shown in FIG. 8, the lower buffer layer 112 hasthe same thickness as the upper interlayer dielectric film 124 or has alarger thickness than the upper interlayer dielectric film 124.Consequently, the multi buffer layer 140, the lower buffer layer 112,the lower gate dielectric film 114, the first and second lowerinterlayer dielectric films 116 and 118, the upper buffer layer 122, andthe upper interlayer dielectric film 124 are removed from the bendingarea BA by the first and second openings 192 and 194. That is, theinorganic dielectric layers 140, 112, 114, 116, 118, 122, and 124, whichform cracks in the bending area BA, are removed from the bending areaBA, whereby the substrate 101 may be easily bent without forming cracks.

As shown in FIG. 7, the signal link 176 may be formed together with thepixel connection electrode 142 through the same mask process as that forforming the pixel connection electrode 142. In this case, the signallink 176 is made of the same material as the pixel connection electrode142, and is formed in the same plane as the pixel connection electrode142, i.e. on the first planarization layer 126. In order to cover thesignal link 176 formed on the first planarization layer 126, the secondplanarization layer 128 is disposed on the signal link 176, or anencapsulation film or an inorganic encapsulation layer constituted by anencapsulation stack including a combination of inorganic or organicencapsulation layers is disposed on the signal link 176, without thesecond planarization layer 128.

In addition, as shown in FIG. 8, the signal link 176 may be formedtogether with the source and drain electrodes 106, 156, 108, and 158through the same mask process as that for forming the source and drainelectrodes 106, 156, 108, and 158. In this case, the signal link 176 ismade of the same material as the source and drain electrodes 106, 156,108, and 158, and is formed in the same plane as the source and drainelectrodes 106, 156, 108, and 158, i.e. on the upper interlayerdielectric film 124. In addition, the signal link 176 is formed on thesubstrate 101 so as to contact the substrate 101. Consequently, thesignal link 176 is formed on the side surface of the upper interlayerdielectric film 124 and the upper surface of the upper buffer layer 122,which are exposed through the first opening 192, and is formed on theside surfaces of the multi buffer layer 140, the lower buffer layer 112,the lower gate dielectric film 114, the first and second lowerinterlayer dielectric films 116 and 118, and the upper buffer layer 122,which are exposed through the second opening 194. As a result, thesignal link 176 is formed in the shape of stairs. In order to cover thesignal link 176 formed in the shape of stairs, at least one of the firstor second planarization layer 126 or 128 is disposed on the signal link176, or an encapsulation film or an inorganic encapsulation layerconstituted by an encapsulation stack including a combination ofinorganic or organic encapsulation layers is disposed on the signal link176 without the first and second planarization layers 126 and 128.

In addition, as shown in FIG. 8, the signal link 176 may be formed onthe multi buffer layer 140. In this case, the multi buffer layer 140disposed between signal links 176 is removed such that the substrate canbe easily bent without forming cracks in the substrate, whereby a trench196, through which the substrate 101 is exposed, is formed between thesignal links 176.

Meanwhile, at least one moisture-blocking hole (not shown) formedthrough the first and second planarization layers 126 and 128 may bedisposed in the bending area BA. The moisture-blocking hole is formed inat least one of a space between the signal links 176 or the upper partsof the signal links 176. The moisture-blocking hole prevents externalmoisture from permeating into the active area AA through at least one ofthe first or second planarization layer 126 or 128 disposed on thesignal link 176. In addition, an inspection line (not shown) that isused during an inspection process is formed so as to have the samestructure as one of the signal links 176 shown in FIGS. 7 to 8.

As described above, the multi buffer layer 140, the lower buffer layer112, the lower gate dielectric film 114, the first and second lowerinterlayer dielectric films 116 and 118, the upper buffer layer 122, andthe upper interlayer dielectric film 124 are removed from the bendingarea BA by the first and second openings 192 and 194. That is, theinorganic dielectric layers 140, 112, 114, 116, 118, 122, and 124, whichform cracks in the bending area BA, are removed from the bending areaBA, whereby the substrate 101 may be easily bent without forming cracks.

FIGS. 9A to 9M are sectional views illustrating a method ofmanufacturing the organic light-emitting display device shown in FIG. 7.

Referring to FIG. 9A, a multi buffer layer 140, a lower buffer layer112, and a polycrystalline semiconductor layer 154 are sequentiallyformed on a substrate 101.

Specifically, SiOx and SiNx are alternately stacked at least once on thesubstrate 101 in order to form a multi buffer layer 140. Subsequently,SiOx or SiNx is deposited on the entire surface of the multi bufferlayer 140 in order to form a lower buffer layer 112. Subsequently, anamorphous silicon thin film is formed on the substrate 101, on which thelower buffer layer 112 is formed, by low-pressure chemical vapordeposition (LPCVD) or plasma-enhanced chemical vapor deposition (PECVD).Subsequently, the amorphous silicon thin film is crystallized into apolycrystalline silicon thin film. The polycrystalline silicon thin filmis patterned through a photolithography and etching process using afirst mask in order to form a polycrystalline semiconductor layer 154.

Referring to FIG. 9B, a lower gate dielectric film 114 is formed on thesubstrate 101, on which the polycrystalline semiconductor layer 154 isformed, and a first gate electrode 152 and a storage lower electrode 182are formed on the lower gate dielectric film 114.

Specifically, an inorganic dielectric material, such as SiNx or SiOx, isdeposited on the entire surface of the substrate 101, on which thepolycrystalline semiconductor layer 154 is formed, in order to form alower gate dielectric film 114. Subsequently, a first conductive layeris deposited on the entire surface of the lower gate dielectric film114, and is patterned through a photolithography and etching processusing a second mask in order to form a first gate electrode 152 and astorage lower electrode 182. Subsequently, the polycrystallinesemiconductor layer 154 is doped with a dopant through a doping processusing the first gate electrode 152 as a mask in order to form source anddrain areas, which do not overlap the first gate electrode 152, and achannel area, which overlaps the first gate electrode 152.

Referring to FIG. 9C, at least one layer of first lower interlayerdielectric film 116 is formed on the substrate 101, on which the firstgate electrode 152 and the storage lower electrode 182 are formed, and astorage upper electrode 184 and a light-blocking layer 178 are formed onthe first lower interlayer dielectric film 116.

Specifically, an inorganic dielectric material, such as SiNx or SiOx, isdeposited on the entire surface of the substrate 101, on which the firstgate electrode 152 and the storage lower electrode 182 are formed, inorder to form a first lower interlayer dielectric film 116.Subsequently, a second conductive layer is deposited on the entiresurface of the first lower interlayer dielectric film 116, and ispatterned through a photolithography and etching process using a thirdmask in order to form a storage upper electrode 184 and a light-blockinglayer 178.

Referring to FIG. 9D, at least one layer of second lower interlayerdielectric film 118 and an upper buffer layer 122 are sequentiallyformed on the substrate 101, on which the storage upper electrode 184and the light-blocking layer 178 are formed, and an oxide semiconductorlayer 104 is formed on the upper buffer layer 122.

Specifically, an inorganic dielectric material, such as SiNx or SiOx, isdeposited on the entire surface of the substrate 101, on which thestorage upper electrode 184 and the light-blocking layer 178 are formed,in order to form a second lower interlayer dielectric film 118.Subsequently, an inorganic dielectric material, such as SiNx or SiOx, isdeposited on the entire surface of the second lower interlayerdielectric film 118 in order to form an upper buffer layer 122.Subsequently, an oxide semiconductor layer 104 is deposited on theentire surface of the upper buffer layer 122, and is patterned through aphotolithography and etching process using a fourth mask in order toform an oxide semiconductor layer 104, which overlaps the light-blockinglayer 178.

Referring to FIG. 9E, an upper gate dielectric pattern 146, a secondgate electrode 102, a first low-potential supply line 162 a, and a firsthigh-potential supply line 172 a are formed on the substrate 101, onwhich the oxide semiconductor layer 104 is formed.

Specifically, an upper gate dielectric film is formed on the substrate101, on which the oxide semiconductor layer 104 is formed, and a thirdconductive layer is formed thereon by deposition, such as sputtering.The upper gate dielectric film is made of an inorganic dielectricmaterial, such as SiOx or SiNx. The third conductive layer is made ofMo, Ti, Cu, AlNd, Al, Cr, or an alloy thereof, and has a single-layeredor multi-layered structure. Subsequently, the third conductive layer andthe upper gate dielectric film are simultaneously patterned through aphotolithography and etching process using a fifth mask in order to forma second gate electrode 102, a first low-potential supply line 162 a,and a first high-potential supply line 172 a and to form an upper gatedielectric pattern 146 thereunder so as to have the same pattern. Atthis time, during dry etching of the upper gate dielectric film, theportion of the oxide semiconductor layer 104 that does not overlap thesecond gate electrode 102 is exposed to plasma, and oxygen in the oxidesemiconductor layer 104 exposed to plasma is removed as the result ofreacting with plasma. Consequently, the portion of the oxidesemiconductor layer 104 that does not overlap the second gate electrode102 becomes a conductor to constitute source and drain areas.

Referring to FIG. 9F, an upper interlayer dielectric film 124, havingtherein a first opening 192, first and second source contact holes 160Sand 110S, first and second drain contact holes 160D and 110D, a firststorage contact hole 188, and first and second line contact holes 164and 174, is formed on the substrate 101, on which the upper gatedielectric pattern 146, the second gate electrode 102, the firstlow-potential supply line 162 a, and the first high-potential supplyline 172 a are formed.

Specifically, an inorganic dielectric material, such as SiNx or SiOx, isdeposited on the entire surface of the substrate 101, on which the uppergate dielectric pattern 146, the second gate electrode 102, the firstlow-potential supply line 162 a, and the first high-potential supplyline 172 a are formed, in order to form an upper interlayer dielectricfilm 124. Subsequently, the upper interlayer dielectric film 124 ispatterned through a photolithography and etching process using a sixthmask in order to form first and second source contact holes 160S and110S, first and second drain contact holes 160D and 110D, a firststorage contact hole 188, and first and second line contact holes 164and 174. In addition, the portion of the upper interlayer dielectricfilm 124 in a bending area BA is removed to form a first opening 192. Atthis time, the first and second source contact holes 160S and 110S, thefirst and second drain contact holes 160D and 110D, the first storagecontact hole 188, the first and second line contact holes 164 and 174,and the first opening 192 are formed through the upper interlayerdielectric film 124 so as to have the same depth.

Referring to FIG. 9G, a second opening 194 is formed in the bending areaBA on the substrate 101, on which the upper interlayer dielectric film124 is formed, and the lower gate dielectric film 114, the first andsecond lower interlayer dielectric films 116 and 118, and the upperbuffer layer 122 in the first source contact hole 160S, the first draincontact hole 160D, and the first storage contact hole 188 areselectively removed.

Specifically, the lower gate dielectric film 114, the first and secondlower interlayer dielectric films 116 and 118, and the upper bufferlayer 122 in the first source contact hole 160S, the first drain contacthole 160D, and the first storage contact hole 188 are selectivelyremoved from the substrate 101, on which the upper interlayer dielectricfilm 124 is formed, through a photolithography and etching process usinga seventh mask. At the same time, the multi buffer layer 140, the lowerbuffer layer 112, the lower gate dielectric film 114, the first andsecond lower interlayer dielectric films 116 and 118, and the upperbuffer layer 122 in the bending area are removed in order to form asecond opening 194. Meanwhile, a portion of the substrate 101 may alsobe removed at the time of forming the second opening 194.

Referring to FIG. 9H, first and second source electrodes 156 and 106,first and second drain electrodes 158 and 108, a storage supply line186, a reference line RL, and a second high-potential supply line 172 bare formed on the substrate 101, on which the second opening 194 isformed.

Specifically, a fourth conductive layer, made of Mo, Ti, Cu, AlNd, Al,Cr, or an alloy thereof, is deposited on the entire surface of thesubstrate 101, on which the second opening 194 is formed. Subsequently,the fourth conductive layer is patterned through a photolithography andetching process using an eighth mask in order to form first and secondsource electrodes 156 and 106, first and second drain electrodes 158 and108, a storage supply line 186, a reference line RL, and a secondhigh-potential supply line 172 b.

Referring to FIG. 9I, a first planarization layer 126 having a firstpixel contact hole 120 is formed on the substrate 101, on which thefirst and second source electrodes 156 and 106, the first and seconddrain electrodes 158 and 108, the storage supply line 186, the referenceline RL, and the second high-potential supply line 172 b are formed.

Specifically, an organic dielectric material, such as an acrylic resin,is applied to the entire surface of the substrate 101, on which thefirst and second source electrodes 156 and 106, the first and seconddrain electrodes 158 and 108, the storage supply line 186, the referenceline RL, and the second high-potential supply line 172 b are formed, inorder to form a first planarization layer 126. Subsequently, the firstplanarization layer 126 is patterned through a photolithography processusing a ninth mask in order to form a first pixel contact hole 120,which extends through the first planarization layer 126. At the sametime, the first line contact hole 164 is formed through the firstplanarization layer 126.

Referring to FIG. 9J, a pixel connection electrode 142, a secondlow-potential supply line 162 b, and a signal link 176 are formed on thesubstrate 101, on which the first planarization layer 126 is formed.

Specifically, a fifth conductive layer, made of Mo, Ti, Cu, AlNd, Al,Cr, or an alloy thereof, is deposited on the entire surface of thesubstrate 101, on which the first planarization layer 126 having thefirst pixel contact hole 120 is formed. Subsequently, the fifthconductive layer is patterned through a photolithography and etchingprocess using a tenth mask in order to form a pixel connection electrode142, a second low-potential supply line 162 b, and a signal link 176.

Referring to FIG. 9K, a second planarization layer 128 having a secondpixel contact hole 144 is formed on the substrate 101, on which thepixel connection electrode 142, the second low-potential supply line 162b, and the signal link 176 are formed.

Specifically, an organic dielectric material, such as an acrylic resin,is deposited on the entire surface of the substrate 101, on which thepixel connection electrode 142, the second low-potential supply line 162b, and the signal link 176 are formed, in order to form a secondplanarization layer 128. Subsequently, the second planarization layer128 is patterned through a photolithography process using an eleventhmask in order to form a second pixel contact hole 144.

Referring to FIG. 9L, an anode 132 is formed on the substrate 101, onwhich the second planarization layer 128 having therein the second pixelcontact hole 144 is formed.

Specifically, a fifth conductive layer is deposited on the entiresurface of the substrate 101, on which the second planarization layer128 having therein the second pixel contact hole 144 is formed. Atransparent conductive film or an opaque conductive film is used as thefifth conductive layer. Subsequently, the fifth conductive layer ispatterned through a photolithography and etching process using a twelfthmask in order to form an anode 132.

Referring to FIG. 9M, a bank 138, an organic light-emitting stack 134,and a cathode 136 are sequentially formed on the substrate 101, on whichthe anode 132 is formed.

Specifically, a photosensitive film for banks is applied to the entiresurface of the substrate 101, on which the anode 132 is formed, and thephotosensitive film for banks is patterned through a photolithographyprocess using a thirteenth mask in order to form a bank 138.Subsequently, an organic light-emitting stack 134 and a cathode 136 aresequentially formed in an active area (AA), excluding a non-active area(NA), through a deposition process using a shadow mask.

According to the present disclosure, as described above, the firstopening 192 in the bending area BA and the second source and draincontact holes 110S and 110D are formed through the same mask process,the second opening 194 in the bending area BA and the first source anddrain contact holes 160S and 160D are formed through the same maskprocess, the first source and first drain electrodes 156 and 158 and thesecond source and second drain electrodes 106 and 108 are formed throughthe same mask process, and the storage contact hole 188 and the firstsource and drain contact holes 160S and 160D are formed through the samemask process, whereby the number of mask processes may be reduced by atleast four compared to the conventional art. In the organiclight-emitting display device according to the present disclosure,therefore, it is possible to eliminate at least four mask processes thatare normally performed in the conventional art, whereby it is possibleto simplify the structure and manufacturing process of the displaydevice and thus to improve productivity.

As is apparent from the above description, according to the presentdisclosure, a second thin film transistor having an oxide semiconductorlayer is applied to a drive transistor of each subpixel, and a firstthin film transistor having a polycrystalline semiconductor layer isapplied to a switching transistor of each subpixel, whereby it ispossible to reduce power consumption. In addition, according to thepresent disclosure, openings disposed in a bending area and a pluralityof contact holes disposed in an active area are formed through the samemask process, whereby the openings and the contact holes have the samedepth. Consequently, it is possible to simplify the structure andmanufacturing process of the display device according to the presentdisclosure and thus to improve productivity. Furthermore, according tothe present invention, a high-potential supply line and a low-potentialsupply line, the voltage difference between which is relatively large,are disposed so as to be spaced apart from each other in the horizontaldirection, whereas a reference line and the low-potential supply line,the voltage difference between which is relatively small, are disposedso as to overlap each other, thereby preventing signal lines from beingshorted.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A display device comprising: a substrate havingan active area and a bending area; a first thin film transistor disposedin the active area, the first thin film transistor having a firstsemiconductor layer; a second thin film transistor disposed in theactive area, the second thin film transistor having a secondsemiconductor layer; a plurality of contact holes disposed in the activearea; at least one opening disposed in the bending area, the at leastone opening having a same depth as at least one of the contact holes; areference line connected to one of the first and second thin filmtransistors; and a low-potential supply line disposed so as to overlapthe reference line.
 2. The display device according to claim 1, whereinthe first semiconductor layer includes a polycrystalline semiconductorlayer and the second semiconductor layer includes an oxide semiconductorlayer.
 3. The display device according to claim 1, wherein the firstthin film transistor comprises a first gate electrode disposed so as tooverlap the first semiconductor layer, a first source electrode disposedso as to contact the first semiconductor layer through a first sourcecontact hole, and a first drain electrode disposed so as to contact thefirst semiconductor layer through a first drain contact hole, the secondthin film transistor comprises a second gate electrode disposed so as tooverlap the second semiconductor layer, a second source electrodedisposed so as to contact the second semiconductor layer through asecond source contact hole, and a second drain electrode disposed so asto contact the second semiconductor layer through a second drain contacthole, and the first and second source electrodes are formed in a sameplane as the first and second drain electrodes, and are made of a samematerial as the first and second drain electrodes.
 4. The display deviceaccording to claim 3, wherein the at least one opening comprises: afirst opening having a same depth as the second source and second draincontact holes; and a second opening having a greater depth than thefirst source and first drain contact holes.
 5. The display deviceaccording to claim 4, further comprising: an upper interlayer dielectricfilm disposed between each of the second source and second drainelectrodes and the second semiconductor layer; and a lower gatedielectric film, a first lower interlayer dielectric film, a secondlower interlayer dielectric film, and an upper buffer layer sequentiallystacked between the first semiconductor layer and the secondsemiconductor layer, wherein the first source and first drain contactholes are formed through the lower gate dielectric film, the first lowerinterlayer dielectric film, the second lower interlayer dielectric film,the upper buffer layer, and the upper interlayer dielectric film inorder to expose the first semiconductor layer, and the second source andsecond drain contact holes are formed through the upper interlayerdielectric film in order to expose the second semiconductor layer. 6.The display device according to claim 5, further comprising: a multibuffer layer disposed on the substrate; and a lower buffer layerdisposed on the multi buffer layer, wherein the first opening is formedthrough the upper interlayer dielectric film disposed in the bendingarea, the second opening is formed through the multi buffer layer, thelower buffer layer, the lower gate dielectric film, the first lowerinterlayer dielectric film, the second lower interlayer dielectric film,and the upper buffer layer disposed in the bending area, and thesubstrate in the bending area is exposed through the first and secondopenings.
 7. The display device according to claim 5, wherein the firstand second source electrodes are formed in a same plane as the first andsecond drain electrodes, i.e. on the upper interlayer dielectric film,and are made of a same material as the first and second drainelectrodes.
 8. The display device according to claim 5, furthercomprising: a storage lower electrode disposed on the lower gatedielectric film; and a storage upper electrode overlapping the storagelower electrode in a state in which the first lower interlayerdielectric film is disposed there between.
 9. The display deviceaccording to claim 8, wherein the storage lower electrode is formed in asame plane as the first gate electrode of the first thin filmtransistor, and is made of a same material as the first gate electrode.10. The display device according to claim 1, further comprising: ahigh-potential supply line spaced apart from the low-potential supplyline in a horizontal direction, wherein a difference between a referencevoltage supplied through the reference line and a low-potential voltagesupplied through the low-potential supply line is less than a differencebetween a high-potential voltage supplied through the high-potentialsupply line and the low-potential voltage supplied through thelow-potential supply line.
 11. The display device according to claim 10,further comprising: an organic light-emitting device comprising an anodeconnected to the second thin film transistor and a cathode connected tothe low-potential supply line, wherein at least one of the low-potentialsupply line or the high-potential supply line is disposed in a meshshape.
 12. The display device according to claim 11, further comprising:a pixel-driving circuit for driving the organic light-emitting device,wherein the pixel-driving circuit comprises: a drive transistorconstituted by the second thin film transistor; a switching transistorconnected to the drive transistor, the switching transistor beingconstituted by the first thin film transistor; a second switchingtransistor constituted by the second thin film transistor, the secondswitching transistor being connected to the reference line; and a thirdswitching transistor constituted by the first thin film transistor, thethird switching transistor being connected to the drive transistor. 13.The display device according to claim 11, further comprising: a firstplanarization layer disposed on an upper interlayer dielectric film; apixel connection electrode disposed on the first planarization layer soas to connect the second thin film transistor and the anode; and asecond planarization layer disposed so as to cover the pixel connectionelectrode.
 14. The display device according to claim 13, furthercomprising: a signal link disposed on the substrate in the bending areaexposed through the at least one opening so as to contact the substrate,the signal link being made of a same material as the first and secondsource electrodes, wherein at least one of the first and secondplanarization layers are disposed so as to cover the signal link. 15.The display device according to claim 13, further comprising: a signallink disposed on the first planarization layer in the bending areaexposed through the at least one opening, the signal link being made ofa same material as the pixel connection electrode, wherein the secondplanarization layer is disposed so as to cover the signal link.
 16. Thedisplay device according to claim 13, wherein the high-potential supplyline comprises first and second high-potential supply lines, whichintersect each other, and the low-potential supply line comprises afirst low-potential supply line disposed parallel to the firsthigh-potential supply line and a second low-potential supply lineoverlapping the reference line in a state in which the firstplanarization layer is disposed there between.
 17. The display deviceaccording to claim 16, wherein the second low-potential supply line isformed in a same plane as the pixel connection electrode, and is made ofa same material as the pixel connection electrode, and the referenceline is formed in a same plane as the second source and second drainelectrodes, and is made of a same material as the second source andsecond drain electrodes.